GFP, also known as green fluorescent protein, is a protein produced by the jellyfish (Aequorea Victoria) that emits bioluminescence in the green zone of the visible spectrum. GFP has become a useful and ubiquitous tool for making chimeric proteins, where it functions as a fluorescent protein tag. It has been expressed in most known cell types and is used as a noninvasive fluorescent marker in living cells and organisms.